Checkboxlist/SelectMany layout tweaks

A checkboxlist/SelectMany property will by default render a single vertically aligned list of checkboxes in the Episerver UI. This is fine for most cases, but depending on how many items you have, you might want to separate them into multiple columns.

Here's a little bit of code that lets you do just that. In the example below, I've added a couple of properties which will use a custom attribute named SelectManyExtended. Notice how you can specify the number of columns.